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CHICAGO PHYSICS 4 Windows on the World Welcome to the fourth issue of Chicago Physics! In our last issue, we took you on a journey to the quantum world. In the current issue, we will guide you to explore the frontiers of our Universe. This year has been an extremely challenging We hope that the stories we share will inspire year forcing all of us to adapt to new realities. you to become more involved and engaged in Despite unprecedented times, we have the Department. Please keep in touch and let achieved much, thanks to the collective us know what you think. efforts of everyone in our department including undergraduate and graduate students, postdocs, the staff and the faculty. Yours sincerely, Special thanks should go to our staff and YOUNG-KEE KIM in the current issue our staff shares some Louis Block Distinguished Service Professor of their experiences in adapting their work Chair, the Department of Physics with students and faculty during these extraordinary circumstances. We also celebrate new members of the Department in this issue. The 4th Maria Goeppert-Mayer Lecture featured Andrea Ghez who was awarded the 2020 Nobel Prize in Physics for discovering the supermassive black hole that lurks at the center of the Milky Way. Her work is nicely connected to the theme of the current issue. The virtual lecture by Ghez, a 1983 graduate of the University of Chicago Laboratory Schools, attracted a diverse audience of about 2,500 people from around the world, including Maria Goeppert-Mayer’s grand-daughter Tania DeBeau, the 1st, 2nd, and 3rd Maria Goeppert- Mayer lecturers (Melissa Franklin, Helen Quinn, and 2018 Nobel Laureate Donna Strickland), Program Director of the Heising- Simons Foundation Cyndi Atherton, Ghez’s mother Susanne Ghez, Ghez’s high school chemistry teacher from the University of Chicago Lab Schools Judy Keane, and Interim Director of the Lab Schools Dave Magill. COVER PHOTO: DAVID MILLER, Professor Department of Physics, the University of Chicago CHICAGO PHYSICS 4 / WINDOWS ON THE WORLD Editor’s Note Contents A century ago to observe the universe was that only very recently have we been able to point an optical telescope at the stars, and to build the first neutrino telescopes. Abby to imagine that visible light interacting with Vieregg explains how rapidly we are moving ordinary matter are the sum contents of our from detection of astrophysical neutrinos Spacetime Singularities and Predictability 4 world. Expanding the observable spectrum to discovering their correlations. The other Robert M. Wald into radio frequencies allowed us to trace our recent “jolt” as Abby describes it is the universe back to the earliest available times remarkable discovery of gravitational waves Opening New Windows on the Universe 6 and understand that it is not in stasis. Hence arising from the merger of massive black Abby Vieregg traditional astronomy gave us the geometry holes and neutron stars – events that appear and some of the history of the universe to be common enough that gravitational Frontiers of Particle Physics 8 David Miller (though there is much more to do), but we wave astronomy is now a burgeoning field. now know it missed out most of the content – (Daniel Holz reported on the initial discovery Honoring the Department of Physics Staff 12 so called “dark matter” and “dark energy”. in Chicago Physics’ inaugural issue.) Black holes represent singularities in the solutions Meanwhile, in quite separately motivated of general relativity which remain mysterious, Adaptations in 2020 14 experiments on earth, we have dissected and Bob Wald presents us with the latest matter in particle colliders to confirm thinking on how lifting the veil on cosmic New Faces 20 the “standard model”, which is a triumph of censorship might enable the construction of unification of three of the four known forces a quantum theory of gravity. For a special Prizes & Awards 22 of nature, yet annoyingly incomplete (no colloquium upcoming this spring, we are gravity) and perfused with parameters whose delighted to welcome back Walter Massey, Events 23 values we cannot predict. who is one of our most distinguished former As physicists, we would like matters to faculty. He is a theoretical physicist whose be more tidy, and the solution is more data. roles have included being Director of Argonne But not just more data in the traditional National Laboratory, Director of the National probes but qualitatively new “windows on Science Foundation, Provost of the University the universe.” In this edition of Chicago of California, President of Morehouse College, Physics, three of our colleagues talk about and President of the School of the Art Institute the new tools we have to observe the fabric of Chicago. of the universe. The particle collider at For us, as for all of you, COVID has made CERN recreates conditions from the early this a challenging year for education, and for universe and while the standard model is our students. Our staff has risen to this now confirmed in all of its ingredients, challenge and tell you here about the efforts David Miller explains how increasing the put in place to mitigate the pandemics resolving power and flux of this instrument impacts, and sometimes how rethinking gives us an opportunity both for precision what we do can deliver unexpected measurements and searching for candidates improvements. Nonetheless, we are looking for dark matter. Neutrinos – the elusive forward to putting the pandemic behind us, particle named by Fermi – are streaming past and consolidating lessons learned. us in high flux, but are so difficult to capture PETER LITTLEWOOD CHICAGO PHYSICS 4 / WINDOWS ON THE WORLD region of spacetime, there should be an accompanying breakdown of predictability. Spacetime Singularities In other words, if it is possible for an observer to “see” a singularity, then even if one is and Predictability given the complete initial conditions of the universe prior to the gravitational collapse, one would not be able to predict what will ROBERT M. WALD happen to observers who go sufficiently far inside of a black hole. The strong cosmic censorship conjecture asserts that, generically, all singularities that result from nonsingular Roger Penrose was awarded the 2020 Nobel Prize in Physics initial data must be of the type that one would fall into them before they can be seen. The first image of a black hole, obtained using Event (shared with Andrea Ghez and Reinhard Genzel) for his ground- Horizon Telescope observations of the center of the galaxy If true, this would mean that there would M87. Credit: Event Horizon Telescope Collaboration breaking work proving that, according to general relativity, be no breakdown of predictability in any singularities must arise in a wide variety of circumstances relevant nonsingular regions of spacetime. It should This can be formulated as follows. The However, for RNdS black holes, quantum to gravitational collapse and to cosmology. However, although be noted that, despite its name, “strong boundary of the predictable region of the effects come to the rescue of strong cosmic cosmic censorship” does not imply “cosmic spacetime is called the Cauchy horizon. censorship. During the past year, Stefan the singularity theorems of Penrose and Hawking establish that censorship,” since strong cosmic censorship The Reissner-Nordstrom and Kerr solutions Hollands, Jochen Zahn, and I showed that, “something must go wrong,” they say very little about the nature of would not preclude a singularity created from have a nonsingular Cauchy horizon. However, within the context of quantum field theory in the singularities. This has remained a major, open issue in general gravitational collapse from extending out to arbitrarily small initial perturbations of curved spacetime, the behavior of quantum distant observers and thus not be confined to these solutions will become singular on the fields near the Cauchy horizon of RNdS black relativity for the past 50 years. a black hole. Cauchy horizon. holes is far more singular than that of classical fields. Even for choices of parameters that The singularity inside of a Schwarzschild Thus, the behavior found in perturbations One very important open issue regarding true, and there are many indirect arguments lead to only very mildly singular behavior black hole (corresponding to a black hole with of the Reissner-Nordstrom and Kerr solutions singularities is whether any singularity arising that support it. However, there is nothing classically, the quantum field behavior is no angular momentum or electric charge) is in support of strong cosmic censorship. from the complete gravitational collapse of a close to a complete proof of this conjecture sufficiently singular that solutions cannot be is of the type compatible with strong cosmic However, a few years ago, an apparent body must always be hidden within a black yet, and, indeed, many mathematicians are extended beyond the Cauchy horizon. censorship. However, the singularities counterexample was found. Consider a hole. By definition, a black hole is a region continuing to build up tools that might help I believe that it may be possible to extend this inside of a Reissner-Nordstrom black hole Reissner-Nordstrom black hole that is put in of spacetime from which it is impossible to tackle this question. argument to completely general spacetimes. (corresponding to a black hole with electric an expanding universe with accelerating escape. If the singularity is contained within If so, this would establish a general version There is a related question about singularities charge) and inside of a Kerr black hole expansion (as we observe in our own a black hole, then—unless we, ourselves, go of strong cosmic censorship in the context of that is also of considerable interest. Suppose (corresponding to a black hole with angular universe). The resulting solution—known as into the black hole—we don’t have to worry quantum field theory in curved spacetime.

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